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limitations of the GPR antenna used for the testing, which is a longer -wave antenna, correlating the <br />dielectric with density data does not provide reliable maps of density in the asphalt. <br />Legend <br />Density (pcf) <br />• 135.0 - 140.0 <br />Q 140.0 - 145.0 <br />d 145.0 - 150.0 <br />• 150.0 + <br />GPR Dielectric <br />+ 4.0 - 4.25 <br />4.25 - 4.5 <br />4.5 - 4.75 <br />4.75 - 5.0 <br />• 5.0 + <br />Figure 10. Map of dielectric and density data collected at Newbury Alcove site in Woodbury, MN <br />However, the nuclear gauge density data can provide useful feedback when viewed alongside other <br />information, such as the results of core testing data from the laboratory. In this study, two rounds of <br />nuclear gauge density testing at a total of 37 locations were conducted in two stages. <br />Results of the initial testing stage are shown in Table 5. For those initial tests at 9 of the 18 test sites, it <br />was observed that densities did not match the cores, as average field densities were observed to range <br />between 85.3 and 97.2 percent of the maximum core density (i.e. all air voids removed) obtained from <br />volumetric testing. Furthermore, the average densities for some locations were unreasonably low. This <br />raised concerns about compaction on municipal roads. <br />To address more general concerns about asphalt compaction — rather than issues specific to chip seal <br />treatments — a second round of nuclear gauge testing was conducted on roads with and without chip <br />seals. The results of the second round of tests are shown in Table 6. <br />The observed densities in the second round of tests were more reasonable. The second round of testing <br />showed that municipal roads had adequate densities in most cases: of the 28 locations in the second <br />round, only two had an average density below 91 percent, and the average maximum density across all <br />locations was 93.3 percent. The second round of testing also indicated that "ordinary" compaction <br />practices in the field produce adequate results. Thus, the cause of stripping is not necessarily related to <br />density if 92 percent field density, as indicated in the MnDOT specification for asphalt compaction, is <br />21 <br />